Formation Of Molecular Complexes Research Articles

Influence of Countercation Hydration Enthalpies on the Formation of Molecular Complexes: A Thorium-Nitrate Example.

The influence of countercations (An+) in directing the composition of monomeric metal-ligand (ML) complexes that precipitate from solution are often overlooked despite the wide usage of An+ in materials synthesis. Herein, we describe a correlation between the composition of ML complexes and A+ hydration enthalpies found for two related series of thorium (Th)-nitrate molecular compounds obtained by evaporating acidic aqueous Th-nitrate solutions in the presence of A+ counterions. Analyses of their chemical composition and solid-state structures demonstrate that A+ not only affects the overall solid-state packing of the Th-nitrato complexes but also influences the composition of the Th-nitrato monomeric anions themselves. Trends in composition and structure are found to correlate with A+ hydration enthalpies, such that the A+ with smaller hydration enthalpies associate with less hydrated and more anionic Th-nitrato complexes. This perspective, broader than the general assumption of size and charge as the dominant influence of An+, opens a new avenue for the design and synthesis of targeted metal-ligand complexes.

Calorimetric and spectroscopic studies of the interaction between zidovudine and human serum albumin

A quantitative analysis of the interaction between zidovudine (AZT) and human serum albumin (HSA) was achieved using Isothermal titration calorimetry (ITC) in combination with fluorescence and 1H NMR spectroscopy. ITC directly measure the heat during a biomolecular binding event and gave us thermodynamic parameters and the characteristic association constant. By fluorescence quenching, the binding parameters of AZT-HSA interaction was determined and location to binding site I of HSA was confirmed. Via T1 NMR selective relaxation time measurements the drug-protein binding extent was evaluated as dissociation constants Kd and the involvement of azido moiety of zidovudine in molecular complex formation was put in evidence. All three methods indicated a very weak binding interaction. The association constant determined by ITC (3.58×102M−1) is supported by fluorescence quenching data (2.74×102M−1). The thermodynamic signature indicates that at least hydrophobic and electrostatic type interactions played a main role in the binding process.

Taming the High Reactivity of Gold(III) Fluoride: Fluorido Gold(III) Complexes with N‐Based Ligands

The synthesis of [NMe4 ][AuF4 ] and [NEt4 ][AuF4 ], as well as an improved one-pot synthesis of Cs[AuF4 ], is reported. The new [AuF4 ]- salts were structurally characterized by single crystal X-ray diffraction, NMR spectroscopy, vibrational spectroscopy, and mass spectrometry. These salts are the first gold(III) fluoride salts that can be isolated in pure form and are convenient to be used in usual organic solvents for subsequent synthesis. The formation of molecular AuF3 complexes in solution is further reported, characterized as [F3 Au(NCCH3 )] at low temperature, as [F3 Au(py)] and a binuclear derivative which are stable at room temperature. The stability of these species in common organic solvents was investigated and they showed a satisfying stability.

Halogen Bonding in the Complexes of CH3I and CCl4 with Oxygen-Containing Halogen-Bond Acceptors.

Methyl iodine (CH3I) and carbon tetrachloride (CCl4) are both important volatile precursors for atmospheric ozone destruction. CH3I and CCl4 can act as halogen bond donors to form molecular complexes with atmospheric organic species, such as 2,5-dihydrofuran, tetrahydrofuran, and acetone. This study characterized the halogen bonds in the CH3I and CCl4 complexes using matrix isolation infrared spectroscopy and density functional theory calculations. With the combination of vibrational frequencies in spectra and the calculated interaction energies, frequencies and atoms-in-molecules analyses, we confirmed the formation of halogen-bonded complexes. CH3I as a halogen-bond donor is comparable or slightly weaker than CCl4, and furans involving ether oxygens are better halogen acceptors than acetone. The results help to understand the possibilities of formation of atmospheric molecular complexes that may influence the atmospheric chemical activities and enhance the aerosol formation.

Effect of oxygen impurity on the efficiency of the formation of complexes with H-bond and aggregation of color centers in lithium fluoride

The effect of impurities on the efficiency of the formation of color centers and hydrogen-bonded molecular complexes upon exposure to various radiations in lithium fluoride crystals grown in air is studied. The results of experiments for measuring optical properties, IR vibrational spectra, luminescence, and thermally stimulated luminescence are presented. The fact that the band in the range of 1800–2300 cm–1 corresponds to stretching vibrations of a complex with strong hydrogen bond is proved based on the Fermi-resonance perturbation in the region of 2080 cm–1, shaped as the Evans hole and bands A, B, and C. It is shown that the composition of these complexes includes an OH– ion and an HF molecule. The crucial role of O2‒ V + oxygen dipoles in the aggregation efficiency and gradient distribution of color centers and radiation resistance of hydroxyl ions is revealed. It is shown that products of radiation decomposition of OH– ions stimulate, while decay of O2‒ V + dipoles suppress, the formation of positively charged color centers.

Verteporfin-induced formation of protein cross-linked oligomers and high molecular weight complexes is mediated by light and leads to cell toxicity

Verteporfin (VP) was first used in Photodynamic therapy, where a non-thermal laser light (689 nm) in the presence of oxygen activates the drug to produce highly reactive oxygen radicals, resulting in local cell and tissue damage. However, it has also been shown that Verteporfin can have non-photoactivated effects such as interference with the YAP-TEAD complex of the HIPPO pathway, resulting in growth inhibition of several neoplasias. More recently, it was proposed that, another non-light mediated effect of VP is the formation of cross-linked oligomers and high molecular weight protein complexes (HMWC) that are hypothesized to interfere with autophagy and cell growth. Here, in a series of experiments, using human uveal melanoma cells (MEL 270), human embryonic kidney cells (HEK) and breast cancer cells (MCF7) we showed that Verteporfin-induced HMWC require the presence of light. Furthermore, we showed that the mechanism of this cross-linking, which involves both singlet oxygen and radical generation, can occur very efficiently even after lysis of the cells, if the lysate is not protected from ambient light. This work offers a better understanding regarding VP’s mechanisms of action and suggests caution when one studies the non-light mediated actions of this drug.

How to Train a Cell-Cutting-Edge Molecular Tools.

In biological systems, the formation of molecular complexes is the currency for all cellular processes. Traditionally, functional experimentation was targeted to single molecular players in order to understand its effects in a cell or animal phenotype. In the last few years, we have been experiencing rapid progress in the development of ground-breaking molecular biology tools that affect the metabolic, structural, morphological, and (epi)genetic instructions of cells by chemical, optical (optogenetic) and mechanical inputs. Such precise dissection of cellular processes is not only essential for a better understanding of biological systems, but will also allow us to better diagnose and fix common dysfunctions. Here, we present several of these emerging and innovative techniques by providing the reader with elegant examples on how these tools have been implemented in cells, and, in some cases, organisms, to unravel molecular processes in minute detail. We also discuss their advantages and disadvantages with particular focus on their translation to multicellular organisms for in vivo spatiotemporal regulation. We envision that further developments of these tools will not only help solve the processes of life, but will give rise to novel clinical and industrial applications.

Calorimetric study of the molecular complex formation of glycyl–glycyl–glycine with 18-crown-6 in aqueous organic solvents

The influence of water–ethanol (H2O–EtOH), water–acetone (H2O–MeAc) and waterdimethylsulfoxide (H2O–DMSO) solvents on the reaction of the molecular complex formation between ether 18-crown-6 (18C6) and small peptide glycyl–glycyl–glycine (3Gly) has been studied at T = 298.15 K. The thermodynamic parameters for the reaction (log K, Δr G, Δr H, Δr S) were obtained from calorimetric titration experiments carried out by means of the calorimetric system TAM III (TA Instruments, USA). The thermodynamics of the [3Gly18C6] molecular complex formation is discussed in comparison with thermodynamic parameters of complex formation between 18C6 and amino acids in mixed solvents using the sоlvation-thermodynamic approach.

Nonlinear diffusion in multicomponent liquid solutions.

Mutual diffusion in multicomponent liquids is studied. It is taken into consideration that the influence of complex formation on the diffusion process may be substantial. The theory is applied to analyze mass transfer in an acetone-chloroform solution. The molecular complex concentration was obtained from the analysis of Fourier transform infrared spectra of this solution. Taking into account molecular complex formation allows one to explain the experimental dependence of diffusion coefficients on the composition (components concentration). The accuracy of experimental and theoretical data descriptions in the frame of our model is compared to the accuracy for some other approaches.

Non-enzymatic glucosylation induced neo-epitopes on human serum albumin: A concentration based study.

Hyperglycaemia induced non enzymatic glycation is accelerated in diabetic patients and aggressively involved in diabetes progression. Human serum albumin (HSA) is the most abundant protein in blood circulation. In hyperglycaemia, it undergoes fast glycation and results in the impairment of structure. Our previous study has demonstrated structural alterations in Amadori-albumin modified with different glucose concentrations from physiological to pathophysiological range. Here, we focused on immunological characterization of Amadori-albumin. Immunogenicity of Amadori-albumin was analysed by direct binding and competitive ELISA. Amadori-albumin was found to be highly immunogenic (expect albumin modified with 5mM) and induced high titre antibodies depending upon the extent of modification. Very high titre antibodies were obtained with albumin modified with 75mM glucose as compared to native albumin. Anti-Amadori-albumin-IgG from rabbit sera exhibited increased recognition of Amadori-albumin than native albumin in competitive immunoassay. Alteration induced in albumin after glucosylation has made it highly immunogenic. Induced antibodies were quite specific for respective immunogens but showed cross-reaction with other Amadori/native proteins. It suggests that glucosylation has generated highly immunogenic epitopes on albumin. Formation of high molecular weight immune complex with retarded mobility further supports specificity of anti-Amadori-albumin-IgG towards Amadori-albumin. It may be concluded that due to early glycation, an array of modification occurred in HSA structure. Such gross structural changes might favour polymerization of most of the native epitopes into potent immunogenic neo-epitopes, but some original epitopes were still active and has contributed in the immunogenicity. It could be concluded that induction of anti-Amadori-albumin antibodies may be due to protection of glucose modified albumin from protiolytic breakdown. We assumed that this type of protein modifications might occur in diabetic patients in hyperglycaemic conditions that may be recognised as foreign molecules and can induce autoantibodies. Increased level of anti-Amadori-albumin autoantibodies may be used as a biomarker in disease diagnosis and its progression.

Synaptic Protein Dynamics Measured by Fluorescence Correlation Spectroscopy

The activity dependent adjustment of synaptic strength (synaptic plasticity) involves the reorganization of post-synaptic proteins. The fast diffusion of synaptic proteins has been shown to play an important role in such molecular rearrangements, but the dynamic events that lead to the formation of molecular complexes are still poorly understood. Taking advantages of Single Particle Tracking (SPT) and FRAP approaches, our group has recently demonstrated that during inhibitory long term potentiation stimuli (iLTP) Gephyrin and GABAA receptors are accumulated at post-synaptic inhibitory sites. In addition we have shown that the synaptic clustering of the scaffold protein gephyrin do not precede the synaptic inclusion of GABA receptors. However, the coordinated dynamics of gephyrin and GABAA receptors outside and inside the synapse remain to be elucidated. To investigate the diffusion dynamics of the main synaptic proteins we exploited here Fluorescence Correlation Spectroscopy (FCS), an established technique to study the mobility of molecules and to measure the protein diffusion parameters with high statistics in unperturbed live cell, in both the plasma membrane and the cytoplasmic space. We calibrated an FCS method (FCS) to study the coordinated multilevel organization of receptors and adhesion molecules that laterally diffuse on the plasma membrane and the scaffold proteins that diffuse in the cytoplasmic space. Our data suggest that, the scaffold protein freely diffuse in the extrasynaptic space and is suddenly immobilized at both synaptic site and extrasynaptic clusters. This approach may clarify the coordinated diffusion of membrane synaptic proteins and cytoplasmic scaffold proteins thus clarifying the mechanisms of synaptic clustering in basal conditions and during synaptic plasticity.

Proteomic analysis to unravel the complex venom proteome of eastern India Naja naja: Correlation of venom composition with its biochemical and pharmacological properties

The complex venom proteome of the eastern India (EI) spectacled cobra (Naja naja) was analyzed using tandem mass spectrometry of cation-exchange venom fractions. About 75% of EI N. naja venom proteins were <18kDa and cationic at physiological pH of blood. SDS-PAGE (non-reduced) analysis indicated that in the native state venom proteins either interacted with each-other or self-aggregated resulting in the formation of higher molecular mass complexes. Proteomic analysis revealed that 43 enzymatic and non-enzymatic proteins in EI N. naja venom with a percent composition of about 28.4% and 71.6% respectively were distributed over 15 venom protein families. The three finger toxins (63.8%) and phospholipase A2s (11.4%) were the most abundant families of non-enzymatic and enzymatic proteins, respectively. nanoLC-ESI-MS/MS analysis demonstrated the occurrence of acetylcholinesterase, phosphodiesterase, cholinesterase and snake venom serine proteases in N. naja venom previously not detected by proteomic analysis. ATPase, ADPase, hyaluronidase, TAME, and BAEE-esterase activities were detected by biochemical analysis; however, due to a limitation in the protein database depository they were not identified in EI N. naja venom by proteomic analysis. The proteome composition of EI N. naja venom was well correlated with its in vitro and in vivo pharmacological properties in experimental animals and envenomed human. Biological significanceProteomic analysis reveals the complex and diverse protein profile of EI N. naja venom which collectively contributes to the severe pathophysiological manifestation upon cobra envenomation. The study has also aided in comprehending the compositional variation in venom proteins of N. naja within the Indian sub-continent. In addition, this study has also identified several enzymes in EI N. naja venom which were previously uncharacterized by proteomic analysis of Naja venom.

Кислотно-основні рівноваги у системах «карбонова кислота – основа – оксиран».

The formation pathways of self- and heteroassociates in the “carboxylic acid – base (tertiary amine / tetraalkylammonium salt) – oxirane” system were investigated. The effect of the steric parameters and solvent characteristics was considered. It was shown that carboxylic acids are highly complexable. The hydrogen-bonded acid dimers, acid – oxirane, and acid – base associates are also capable to form secondary complexes. The dependence of processes of primary and secondary association on solvent polarity and acid-base properties of system components was established. It was stated that the inert aprotic solvents promote primary and secondary complex formation in the “carboxylic acid – base – oxirane” system, but the primary association is the dominant interaction process. The effect of the nucleophilic and base properties of organic nitrogen-containing base on the association degree of the system components was estimated. The decrease of steric hindrances at the nitrogen atom in the base results in decrease of concentration of the complex acid – base, and the temperature decrease has similarly effect. It was established that more nucleophilic and more polar then amines, quaternary ammonium salts tend to form ionic complexes, yet increase of system temperature shifts the equilibrium towards formation of molecular complexes. The existence of all the considered types of hydrogen-bonded complexes was confirmed by experimental spectral methods: IR and UV spectroscopy. The spectroscopic studies were carried in two solvents: non-polar aprotic carbon tetrachloride and polar aprotic epichlorohydrin. The quantitative characteristics of complexes: acid – acid, acid – oxirane, acid – base and their effect on reaction rate and its mechanism were analyzed.

Theoretical investigation of gas-phase molecular complex formation between 2-hydroxy thiophenol and a water molecule.

The torsional potential of OH and SH rotations in 2-hydroxy thiophenol is systematically studied using the MP2 ab initio method. The outcome of state-of-the-art calculations is used in the investigation of the structures and conformational preferences of 2-hydroxy thiophenol and aims at further interaction studies with a gas phase water molecule. SCS-MP2 and CCSD(T) complete basis set (CBS) limit interaction energies for these complexes are presented. The SCS-MP2/CBS limit is achieved using various two-point extrapolation methods with aug-cc-pVDZ and aug-cc-pVTZ basis sets. The CCSD(T) correction term is determined as the difference between CCSD(T) and SCS-MP2 interaction energies calculated using a smaller basis set. The effect of counterpoise correction on the extrapolation to the CBS limit is discussed. The performance of DFT based wB97XD, M06-2X and B3LYP-D3 functionals is tested against the benchmark energy from ab initio calculations. Hydrogen bond interactions are characterized by carrying out QTAIM, NCIPLOT, NBO and SAPT analyses.

Photosensitizing properties of supramolecular systems based on chlorin e6

The novel supramolecular systems based on chlorine e 6 (Ce 6 ) are presented, and their optical absorption and fluorescence have been investigated. The influence of different excipients as poly-N-vinylpyrrolidone (PVP), polyethyleneglycol (PEG), bovine serum albumin (BSA), chitosan, Triton X-100 (TX-100) on spectral characteristics of these systems has been studied. The obtained spectral-fluorescence characteristics of Ce 6 -PVP, Ce 6 -PEG, Ce 6 -BSA, Ce 6 -TX-100 indicate disaggregation of chlorine e 6 molecules and their consecutive interaction with excipients in solutions and formation of molecular associates and molecular complexes. The system Ce 6 -chitosan is characterized by aggregation of pigments in solution that reduces photochemical activity of a photosensitizer. The fluorescence quantum yield j k of mentioned above supramolecular systems has been calculated. The results can be useful during the new method of controlled aggregation of photosensitizers as a part of supramolecular complexes development as well as for the purposes of new medicines of predictable photodynamic activity creation.

Fermi resonance of molecular complexes with strong hydrogen bond in irradiated LiF:OH crystals

Evidence for the formation of molecular complexes with strong hydrogen bond with fluorine in lithium fluoride crystals containing impurities of OH̄ ions and magnesium under the action of irradiation are presented. The proofs are based on Fermi resonance perturbation of IR stretching vibration bands in the region of 1800–2300cm−1. It is established for the first time that the profile of the stretching vibration bands has three types of perturbations owing to Fermi resonance of stretching vibrations with its overtones: (1) the effect on the band profile without perturbation; (2) “Evans hole” at 2080cm−1; (3) A, B, C bands. Manifestation of these particularities depends on a dose and conditions of a crystal irradiation. It is shown that the IR spectra recorded at a helium temperature confirm that the centers with bands at 1800–2300cm−1 belong to the complexes with hydrogen bond. It is proposed that the OH̄ ion, HF molecule and fluorine ion to be considered as the main structural units of the complex.

MOLECULAR COMPLEXES OF SULPHUR DIOXIDE WITH N,O-CONTAINING ORGANIC BASES (REVIEW)

The literature data on the synthesis, stoichiometry, structure and relative stability of molecular complexes of sulphur dioxide with N,O-containing organic bases have been systematized and generalized. It was shown that the yield of the reaction product of sulfur dioxide with organic bases (such as amines) are strongly influenced by the conditions of synthesis: the nature of the solvent (basicity, polarity), the temperature and SO2:L ratio in the reaction medium. The stoichiometry of SO2*nL molecular complexes depends on ligand denticity, as well as its ability to H-bonding. The reaction of the sulfur oxide (IV) with organic bases can give S←N and S←O complexes. With the increase of the value of base proton affinity the decrease ΔrSN values has been marked. Characteristic parameter Δr SN = r SN – a1(rS+ rN) (where rSNis the S←N donor-acceptor bond length) has been determined by microwave spectroscopy and X-ray analysis, rSand rNwere the tabulated values of the homopolar covalent radii of sulphur and nitrogen heteroatoms. The dependence of formation enthalpy of molecular complexes of basic amines and spectral characteristics has been noted; enthalpy-entropy compensation for S←N and S←O complex-es has been stated. Despite the limited experimental data on the thermodynamics of complex formation and the lengths of donor-acceptor bonds for the same compounds it has been found bond S←N strength in SO2 molecular complexes to depend on the intrinsic value of ΔrSN. The contribution of van der Waals forces and charge transfer forces to the formation of molecular complexes of sulphur dioxide has been stated.

Muramyl peptides activate innate immunity conjointly via YB1 and NOD2.

Bacterial cell wall muramyl dipeptide (MDP) and glucosaminyl-MDP (GMDP) are potent activators of innate immunity. Two receptor targets, NOD2 and YB1, have been reported; we investigated potential overlap of NOD2 and YB1 pathways. Separate knockdown of NOD2 and YB1 demonstrates that both contribute to GMDP induction of NF-κB expression, a marker of innate immunity, although excess YB1 led to induction in the absence of NOD2. YB1 and NOD2 co-migrated on sucrose gradient centrifugation, and GMDP addition led to the formation of higher molecular mass complexes containing both YB1 and NOD2. Co-immunoprecipitation demonstrated a direct interaction between YB1 and NOD2, a major recombinant fragment of NOD2 (NACHT-LRR) bound to YB1, and complex formation was stimulated by GMDP. We also report subcellular colocalization of NOD2 and YB1. Although YB1 may have other binding partners in addition to NOD2, maximal innate immunity activation by muramyl peptides is mediated via an interaction between YB1 and NOD2.

Enantioselective Keto–Enol Tautomerism of 3-Hydroxyflavones Upon Molecular Complex Formation of Their α-Diketo Forms with Carbohydrates in Aqueous Solutions

Complementary physicochemical methods (UV, IR, ORD) found that the α-diketo tautomer of 3-hydroxyflavones formed complexes with carbohydrates in water. The contribution of the flavone α-diketone increased sharply because it was stabilized after reacting with a carbohydrate cis-diol. The newly formed chiral center of the tautomeric diketo flavones was induced asymmetrically. The complexing ability of the carbohydrates was inversely proportional to their degree of hydration (and decreased in the order maltoseglucose-galactose-arabinose).

Erratum to: Application of isothermal titration calorimetry for evaluation of water–acetone and water-dimethylsulfoxide solvents influence on the molecular complex formation between 18-crown-6 and triglycine at 298.15 K

Erratum to: Application of isothermal titration calorimetry for evaluation of water–acetone and water-dimethylsulfoxide solvents influence on the molecular complex formation between 18-crown-6 and triglycine at 298.15 K